1. Field of the Invention
The present invention relates to an electronic timepiece such as a quartz timepiece, and the like.
2. Description of the Related Art
There are known conventional electronic timepieces, such as quartz timepieces, that use an electronic circuit to generate accurate, periodic electrical signals measure the passage of time and to display the time.
Similarly to mechanical wristwatches in wristwatches that use these electronic timepieces, it is desirable to make a timepiece movement small and thin in size. However, the size of a power supply is determined from a relationship between the power consumption (usually in terms of electric current) of a timepiece and the capacity of the power supply to meet the timepiece's power requirements while satisfying an expected life span for the power supply. Accordingly at present, the thickness of the timepiece movement of an electronic timepiece is dominated by the thickness of the power supply unit.
In electronic timepieces, the power supply is used as a drive source for driving the electrical components. This power supply is typically arranged such that a positive pole is grounded to the case side of the timepiece and a negative pole is in contact with an electrode disposed as a power rail to the electrical components of the movement.
One surface of a negative power rail terminal, which is the electrode disposed as a power rail to the electrical components of the movement, is in contact with the negative pole of the power supply as described above, and the other surface of the negative power rail terminal is disposed in facing a dial plate. When the dial plate comes into contact with the negative power terminal, an electric short-circuit between the positive and negative poles of the power supply is established because the dial plate is formed of a metal material and is in contact with the case. As a result, drain of power is intensively consumed from the power supply, and the power current is diverted away from the electrical components giving rise to a problem that the hands of the timepiece, and other electronically controlled components, are stopped. To cope with this problem, an insulation sheet is interposed between the above-described negative power rail terminal and the dial plate.
As shown in (1) Japanese Unexamined Utility Model Publication Nos. 63-3059 and 58-71977, the insulating structure of the negative power rail terminal is arranged such that a power supply is accommodated in a power-supply-accommodation recess formed in a main plate acting as the base frame of a timepiece and an insulation-sheet-accommodation recess is further formed in the power-supply-accommodation recess. Slits or pins are disposed around the outer periphery of the insulation-sheet-accommodation recess. To attach a thin insulation sheet, it is positioned by the slits or the pins as well as accommodated in the insulation-sheet-accommodation recess so that it exactly fits therein in a surface direction, thereby electric short-circuit between the negative power rail terminal and the dial plate or an hour wheel presser, each composed of a metal material, is prevented.
Further, an hour wheel presser is used to provide a predetermined play (movable back-lush in an axial direction) with an hour wheel acting as a time-display wheel disposed in the movement.
As disclosed in (2) Japanese Unexamined Utility Model Publication No. 04-029891, an hour wheel presser guides an hour wheel in its axial direction. According to this publication, the hour wheel presser is fixed on the upper surface of a movement by a bonding or screw system, or a press-fit engaging system. Further, a dial plate is disposed on the upper surface of the hour wheel presser, and the insulation sheet is interposed between the hour wheel presser and the dial plate.
In the insulating structure of (1), however, the insulation sheet is thin. Thus, a problem arises in that it is difficult to attach the insulation sheet to the slits or the pins to position it, and the assembling property thereof is bad. In particular, since the insulation sheet is thin and does not have rigidity, even if it is attached to the slits or the like while it is being assembled to the movement, there is a possibility that it may be removed or dislocated by a slight shock, and the like. When a power supply is assembled in this state, a problem arises in that electric short-circuit is caused by the contact of a member set to the negative potential of the power supply with a member set to the positive potential of the power supply and the operation of hands is stopped.
Further, when the hour wheel presser is fixed by the boding system in (2), a problem arises in that a bonding agent is applied in an excessively large amount and protrudes to the periphery thereof and that an assembly time is increased because a curing time of the bonding agent is necessary. Further, since hour wheel presser is fixed by the application of the boding agent, the thickness of the applied bonding agent is dispersed, which results in an inevitable increase in the dispersion of plays of hour wheels. Further, since the insulation sheet is fixed by the application of the bonding agent, when the insulation sheet is picked up and pressed to a predetermined position, it is dislocated therefrom or deformed, thereby the outside appearance of the movement is defaced.
When the hour wheel presser is fixed by the screw system, two or more screws are necessary because it cannot be fixed by one screw. Thus, the number of screws is increased as well as a troublesome job for assembling the screw pins to a main plate is additionally needed, thereby an assembly job becomes complex and cost is increased thereby.
Further, when the hour wheel presser is fixed by the press-fit engaging system, the number of parts is reduced as compared with the screw system and workability in assembly is improved. However, a synthetic resin portion is cut by the hour wheel presser composed of a metal material, and synthetic resin powder having been cut is deposited on a train wheel portion. As a result, a problem arises in that the operation of the hands is delayed or stopped.
Further, since two kinds of parts, that is, a dedicated hour wheel presser and a dedicated insulation sheet are used conventionally, the number of parts is increased as well as the production and management of them are troublesome and cost is increased.